Ultrafast Dynamics of the Indoline Dye D149 on Mesoporous ZnO and Al2O3 Thin Films
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Oliver Flender
Abstract
Ultrafast photoinduced electron injection and subsequent relaxation steps of the indoline dye D149 were investigated for mesoporous thin films using pump–supercontinuum probe (PSCP) transient absorption spectroscopy in the range 370–770 nm. Three types of mesoporous ZnO layers were compared: Electrodeposited ZnO thin films prepared by using the structure-directing agents (1) Eosin Y (EY) and (2) Coumarin 343 (C343), which are known to produce ZnO layers of different morphology; and (3) mesoporous ZnO thin films consisting of sintered nanoparticles with a diameter of 20 nm. As a reference system, we used a “non-injecting” mesoporous thin film with large band-gap, consisting of Al2O3 nanoparticles with a diameter of 50 nm. On all ZnO thin films, D149 efficiently injects electrons. We observed two components, a dominant one with τ ≤ 70 fs (time-resolution-limited) and a slower one with a time constant of 250–350 fs. Fast initial charge separation is also consistent with the immediate appearance of oscillatory structure due to a change in refractive index of ZnO upon electron injection. For all ZnO thin films, we observe a transient shift of the spectra with a time constant of ca. 20 ps which is assigned to a transient Stark effect (= electrochromism). The S0 → S1 absorption band of D149 is shifted due to the build-up of a local electric field between dye radical cations and ZnO conduction band electrons. On longer timescales, step-scan FTIR spectroscopy revealed a slightly faster cation-electron recombination on ZnO/C343 than on ZnO/EY thin films. On Al2O3, metastable close cation-electron pairs are formed initially which recombine afterwards, and no transient Stark effect is observed. Complementary PSCP experiments on D149 in the ionic liquid [C2mim]+ [N(CN)2]– show that D149 is ideally suited for solar cell applications because of its long S1 lifetime of 590 ps. In addition, biphasic solvation dynamics are observed in this IL with a subpicosecond component and a much slower component related to the viscosity of the IL which is well described by a stretched exponential.
Acknowledgement
We thank Johannes R. Klein for extensive help during the preparation of the thin film samples and the PSCP experiments. Optical microscope pictures of the ZnO thin films were kindly provided by C. Pritzel and H. F. R. Trettin. We thank G. Boschloo (University of Uppsala, Sweden) and R. Oswald (University of Göttingen) for many valuable discussions and support. We are also grateful to N. P. Ernsting (Humboldt University Berlin, Germany) and J. L. Pérez Lustres (University of Santiago de Compostela, Spain) for their continuous support and advice.
©2015 Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Frontmatter
- Preface
- Congratulations to Jürgen Troe
- The Kinetics of the Reaction C2H5• + HI → C2H6 + I• over an Extended Temperature Range (213–623 K): Experiment and Modeling
- Collisional Relaxation of NCN: An Experimental Study with Laser-Induced Fluorescence
- Reaction of Chlorine Molecules with Unsaturated Submicron Organic Particles
- Theoretical Kinetics Study of the Reactions Forming the ClCO Radical Cycle in the Middle Atmosphere of Venus
- On the Relation between Population Kinetics and State-to-State Rate Coefficients for Vibrational Energy Transfer
- Investigation of the ν2 + 2ν3 Subband in the Overtone Icosad of 13CH4 by Pulsed Supersonic Jet and Diode Laser Cavity Ring-Down Spectroscopy: Partial Rovibrational Analysis and Nuclear Spin Symmetry Conservation
- The Rotationally-Resolved Absorption Spectrum of Formaldehyde from 6547 to 7051 cm−1
- Constraining the Conformational Landscape of a Polyether Building Block by Raman Jet Spectroscopy
- The Reaction Kinetics of Amino Radicals with Sulfur Dioxide
- Challenging High-Level ab initio Rovibrational Spectroscopy: The Nitrous Oxide Molecule
- Reaction of the CF3 Radical with Various Cations (Ar+, Xe+, O2+, NO+, CO2+, C2F5+)
- Electronic Spectra of Corannulenic Cations and Neutrals in Neon Matrices and Protonated Corannulene in the Gas Phase at 15 K
- Photoionization Yields in Intense fs-Laser Fields – A Systematic Investigation of Chirp Effects
- Determination of the Temperature-Dependent OH− (H2O) + CH3I Rate Constant by Experiment and Simulation
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- Multiphoton Ionization of Liquid-to-Supercritical Methanol. Ultrafast Dynamics of Electron Localization and Geminate Recombination
- Femtosecond Infrared Spectroscopy of Aroylperoxide Photofragmentation – Site Selective Decarboxylation
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- Complexation and Chiral Recognition of Chiral Binaphthyl Derivatives and β-Cyclodextrins in Solution Probed by Triplet Excited State Relaxation
- Ionic Solutions Probed by Resonant Inelastic X-ray Scattering
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- Investigation of the Growth Behaviour of Cobalt Thin Films from Chemical Vapour Deposition, Using Directly Coupled X-ray Photoelectron Spectroscopy
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- Observation of Translation-to-Vibration Excitation in Acetylene Scattering from Au(111): A REMPI Based Approach
